A robot can be described as humanoid when it possesses certain attributes of the appearance and functionalities of man: a head, a trunk, two arms, two hands, two legs, two feet, etc. Beyond appearance, the functions that a humanoid robot is capable of fulfilling will depend on its ability to perform movements, to speak and to “reason”. Humanoid robots are capable of walking, of making gestures, with the limbs or with the head. The complexity of the gestures that they are capable of performing is ever increasing. However, robots remain fragile, notably on account of the motors of their articulations. This fragility is a significant handicap for the development of mass-market applications. Indeed, within the context of these applications, it is particularly deleterious to have to cope with breakages or faults due to repeated falls since it would be necessary for producers and distributors of humanoid robots to deploy an after-sales service of disproportionate significance to the initial sales, and at an unacceptable cost to the public at large.
A first strategy applicable to humanoid robots endowed with a walking capability for minimizing the risks of falls is to ensure that said walking is sufficiently stable. A widely used means for doing this is to adjust the trajectory of the robot in such way that the Zero Moment Point (ZMP) (i.e. the point on the ground where the moment of the bearing axis and the moment of the azimuth axis are zero) is included in the robot's support polygon (i.e. in the case of a walking robot, if the latter is standing on one foot, the support polygon will have the shape of this foot. If it is standing on its two feet, the area of this polygon will be that of the two feet, plus the interpodal area.) This strategy is however not sufficient to ensure stability of the robot under all conditions, notably in cases where the robot has to advance over an uneven terrain, perform movements which place it at a limit of equilibrium or sustain knocks caused by third parties.
Conventional solutions to this problem use common principles comprising verifying that the projection of the center of mass of the robot on the surface of advancement remains included in the support polygon for the robot and then, in the case of exiting of said center of mass from said polygon, to determine the best fall posture as a function of the angle of exit of said polygon. These solutions operate correctly in the simple case of a static robot endowed with sensors making it possible to decide without ambiguity that the robot is in a fall position. The same does not hold in the case of robots while walking, notably when said fall detection sensors may confuse a normal gesture included in the walking trajectory and the onset of a fall. Indeed, in this case, mechanisms for protecting against falls will be triggered inappropriately whereas there is no reason to interrupt the normal course of the robot's activities.